Topic: K5 750 weird problem/SOLVED!

[my name is nobody]

Hoping you guys can help, I'm at wits end. What could cause a drivability issue that mocks/mimics a "running out of gas"symptom? (feels like the petcock needs to be switched to reserve, except the tank is full).....This starts just as the engine reaches normal operating temp, and the bike is accelerated to around 60 mph. The symptom begins then and continues until bike is shut down, and allowed to cool off. I have tried so many things to fix this problem, that I can't remember everything
I've done. If anyone could give some suggestions as where to look or what to look for, things you've seen, I'd REALLY appreciate it. This is a weird one that I have spent uncanny amounts of time on, and to no avail. I have done the obvious,
like opening the gas cap, clear tube method, etc. I know there is an answer, But damned if I know what it is. Partial list:
2 sets of carbs
charging system seems ok..haven't gone there yet, but no dead battery/electrical issues
checked petcock flow, seems constant (single hose type)
no garbage in tank
bypassed kill switch
bypassed ign switch
several condensers
2 sets of coils
new wiring harness (o.e was in bad condition)
This thread could go on and on. I will try to keep with it. This seems like a fuel issue (first impression)
but everything I've tried or substituted hasn't worked. Maybe throw out some simple stuff that I haven't thought of... thanks folks..jim

[Airborne 82nd]

check to make sure gas cap vent is open.

[jgger]

Check your plugs when it goes weird on you. If they are dry it is probably in the fuel delivery. If they are wet it would lean toward electrical  (spark .shutting down).

You don't have anything that might be choking the air off, do you? Something flapping around or covering the air box.

[my name is nobody]

check to make sure gas cap vent is open.

Opened cap, no effect

Check your plugs when it goes weird on you. If they are dry it is probably in the fuel delivery. If they are wet it would lean toward electrical  (spark .shutting down).

will check and report findings


You don't have anything that might be choking the air off, do you? Something flapping around or covering the air box.

No obstructions at airbox, stock filter, bike is all 100% stock. maybe turn petcock off when problem occurs and check bowls
for low fuel while checking plugs?

[disco]

Turning off the fuel tap, when problem occurs & checking the fuel level in bowls sounds like a good idea. At least it will give you a clue as whether it’s fuel or spark.

There’s not a clogged in-line fuel filter downstream of fuel tap is there?

[pjlogue]

I had the exact same symptoms after my restoration.  It turned out to be the fuel line and filter.  I had the line and filter going down below the bowls of the carb and then to the fuel inlets.  The heat from the cylinders was causing a vapor lock in the filter.  (after the engine got to running temp I would see an air pocket in the clear fuel filter)  Got rid of the filters and routed the line from the petcock spigot through the holes in the carb bank mounting plate directly to the inlet pipe for the carbs. 

Any configuration I have tried where the fuel line has a "n" in the line, where the line bends up and then back down and / or any filter in the line has caused problems.  The problems are most notable in warm weather as well and I suspect it is vaporizing fuel in the line to cause a vapor lock.  Even a small bubble in the top of the "n" can restrict the fuel flow enough at highway speed to cause problems.  The flow in a 5.5mm tube isn't fast enough to flush out the bubble.

Rust in the tank can clog the screen in the tank if you have a stock fuel petcock.  Also old fuel lines can deteriorate and clog the tiny inlet screens in the fuel float valves. 

-P.

[MoMo]

Take the petcock apart and check it. Also, make sure the vacuum line to the petcock is not kinked. I had both problems with Kawasaki( Ninja 600 and KZ1000)...Larry

[my name is nobody]

Disco, pj, and mo.......thanks guys, you got me thinking with your suggestions. I don't have in line filters, but I could install
clear fuel line and watch what is happening to some degree. Will get some clear line this week and report back my findings.
Again, much appreciated!

[my name is nobody]

Just wrote an update, but it disappeared............Just playing around, I've been able to affect things (for the better) at times
by re routing/trimming existing hoses. 2 of 3 test drives have been un eventful. Have found a section of hose assy. to be
in the shape of an "N" (sort of) and re routing hoses has yielded positive results. Will report findings when I nail the problem
for good. Thank you Gentlemen, I think I see light at the end of the tunnel

[my name is nobody]

looking farther, I discovered one pair of carbs MAY, (not sure yet), have the wrong size fuel joiner pipe. I have 550 and 750
carb parts scattered about and may have installed a wrong size tee in my 750. tees are different between the two models, and may be cause of my drivability issue. I have been able to actually affect the symptoms recently by re routing hoses and watching flow rate. still looking tho, hope this will help someone. Will post soon as I have definite answer.

[my name is nobody]

First, thanks to all who posted....Rather than go into a long winded step by step procedure, the driveability issue I was
chasing turned out to be caused by the fuel line I was using. I can't begin to imagine WHY the existing line caused problems,
as I can see absolutely no issues with it. It is Genuine Honda fuel line, sold to me by a member here, and came in Honda pack
aging. I cut the tubing lengthwise and looked for deterioration, blockages, rot, blew air thru it, nothing wrong. I replaced it with some garden tractor/universal type stuff (for now) and both carb pairs fill with gas as they are supposed to. The only thing I can figure is the old line was maybe sucking air at the tee fittings. Each time the lines were moved, the flow rate changed ,sometimes to a trickle. My test drive results reflected this as well. It made sense anyway.. The clear line that is
on there now is a slight bit smaller in I.D., but it seals very well at the tees. The test drives were all successful. Routing is
stock k5 again, with the petcock outlet hose a little bit longer than before, forming a downward dip (kind of like a drain trap), before going thru the hole in the carb stay plate. Worked like a charm, and the bike loves it. Thanks again folks